An expert has accepted the invitation to review the manuscript. Can the other one still review the manuscript?

I'm not sure about the background and situation of your question, but generally speaking, after one expert accepts the invitation to review the manuscript, whether another expert can review the manuscript depends on the specific situation.

In some cases, the expert invited to review the manuscript may be unable to complete the task for some reason, and another expert may be invited to review the manuscript. However, it is usually necessary to ensure that the professional fields of two experts and the opinions of peer review will not conflict or repeat, so as to ensure the fairness and accuracy of peer review.

So if you want to know more specific information, it is recommended to consult the editor who invited the comments.